The present invention relates to a corn-based mixed diet comprising rumen-protected lysine (hereinafter referred to as "RPLys"), rumen-protected methionine (hereinafter referred to as "RPMet") and appetizer having a flavor which meets the dairy cow's taste, and a feeding method for dairy cows with the diet.
Investigations have been made hitherto for the purpose of improving the dairy cow breed and developing diets for the dairy cows in order to increase the milk production and to improve the milk qualities such as proteins and fats contained in the milk. As a result, high-yielding dairy cows capable of producing 7500 kg or more of milk a year and, particularly, those capable of producing 10,000 kg or more of milk a year were bred. Protein balance attracted attention in increasing the milk production and keeping good health of dairy cows, and after investigations of them, American NRC standard was established. In order to keep the milk production stable while keeping a high quality thereof, various nutritive substances and at least one of protein sources such as grains, fish meal and blood meal are incorporated as additives for grass into the dairy cows diet. However, such protein sources do not always meet the dairy cows' taste and the intake of such additives poses a problem of a load in the metabolism of the diary cows. Thus the administration of protein by feeding easily available protein sources is not always helpful to the efficient milk production.
Investigations were made for the purpose of direct administration of the amino acids constituting the protein under these circumstances. However, when the amino acids are directly mixed in the diet and given to the dairy cows, most of them are degraded in the rumen of cows before they reach into the small intestine where they are to be absorbed, and thus the purpose cannot be attained. Thereafter, rumen-protected amino acids (RPAA) were developed, which are prepared by coating the amino acids with a protecting agent so that they are not degraded in the rumen and the amino acids are reached and exposed in the small intestine. In particular, RPMet (rumen-protected methionine), RPLys (rumen-protected lysine) and RPMet & RPLys (rumen-protected methionine and lysine) are known.
As for the causal relation between the milk quality and the amino acids, it was found from the infusion experiments in which the amino acids are directly infused into the small intestine via duodenal cannula that especially methionine and lysine among the amino acids have a close relation to the milk quality. It is known that methionine is effective in improving the fat content in the milk and lysine is effective in improving the protein content in the milk.
J. A. Rogers et al. made experiments in which two kinds of corn-based diets containing both RPMet and RPLys were given to dairy cows to compare the relationships between the diet and the milk production of them with each other (Journal of Dairy Science, Vol. 72, No. 7, 1989). In the experiments, nine levels of RPAA were used, which were prepared by mixing one of three levels (3.4, 7.8 and 12.2 g/d) of RPMet with also one of three levels (5.9, 13.5 and 21.1 g/d) of RPLys. The diets comprised corn silage and corn grains as the bases. One kind of the diets further contained corn gluten meal and urea, and the other contained soybean meal. The former was given to low-yielding dairy cows with a milk production of 7,500 kg or below per year, and the latter was given to high-yielding dairy cows of a milk production of 8,000 kg or above per year. Each of the nine levels of RPAA was added to each of the two kinds of diets. Urea was used as the nitrogen source for the microorganisms which accelerates the digestion of the diet in the rumen. Since urea is degraded in the rumen, it does not reach the small intestine. It is usually said, therefore, that urea has no effect of improving the protein content in the milk, since it is not absorbed in the dairy cow's body. J. A. Rogers et al. reported that neither milk production nor milk protein had been improved by the soybean meal diet in the high-yielding dairy cow groups. Although they reported also that the milk production in the low-yielding group to which the corn gluten diet had been given was increased by 3%, the yield was yet below the level of the high, stable milk production.
On the other hand, Sato et al. reported at International Dairy Congress in October, 1990 that the fat content of the milk had been improved by giving a corn-based diet containing RPLys and RPMet to dairy cows. However, they were silent on the method of feeding dairy cows for increasing further the milk production of the high-yielding dairy cows evenly and steadily. Also, they did not disclose the incorporation of the appetizer into the corn-based mixed diet.
As for the milk production of the high-yielding dairy cows in the course of feeding them, it varies depending on the difference in individual cows at present and, therefore, it is impossible for the dairy farmers to accurately estimate the milk production per year at the start of feeding the high-yielding dairy cows, which is a cause for the instability of the management of the dairy farmers. Under these circumstances, it is demanded to develop methods for the stable feeding of high-yielding dairy cows and also for the high milk production by eliminating the individual difference of the cows so that the milk production per year can be accurately estimated from the number of the cows.